Process for preventing corrosion



Patented May 26, 1953 Masters --UNIIQ STATES ()FFi-CE No Drawing. ,fipplieatiun -May'fi, 1951, Serial N0. 227,944

*Claims. l

invention relates to the inhibition of cor 51 051011 oi metals, andparticularlyto a compositionior use, in preventin corrosionof metals and particularly iron,-steel,l-and ierrcus alloys. The .corrosioniinhibitors contemplated hereinifind special utility in the prevention of corrosion.of,pipe or equipment which is in contact with a corrosive oil-containing medium, as, for example, in oil wells producing corrosive oil or oil-brine mixtures, in refineries-and the like. Our inhibitors may, however, be used in other systems or applications. They appear to possess properties which impart to metals resistance to attack by a variety of corrosive agents, such as brines, weak inorganic acids, organic acids,"C'O2, H28, 02, etc.

In its broadest aspects our-invention contemplates a process for preventing corrosion of metals, comprising :the step of applying to such metals a substituted tetrahydropyrimidine of the formula type:

N-om

R-C CB2 where ,D is a. member of the class consisting of 'D R andfR; 13' "represents 'a divalent organic iradical :containingiess than 25 carbon atoms, composed of elements from 'theygroupconszsting of 'jC,,I-I, O, and :N; R is amember oftheolass consisting of hydrogen andhydrocarbonradicals, with the proviso1.that at least 10118 ocourrenoepf R, :containsfrom 8 to $32 carbonatoms; Blis a member of the class consisting of hydrogen and hydrocarbon radicals containinglessthanq carigbon :atoms, with the proviso that ,atlleast three occurrences, of B .be hydrogen. ,A simple example nfra compound of this typelis. shown inxthe "for- ,gmnlaibelow which is .that forl2+octylrtetrahydropyrimidine and in ,whichtheelements ofthe ring are numbered to conform to .the conventional numbering system.

radical appears 'as a substituent of the Z-carbon.

idine will contain :a.2-substituent consisting of a atom of the tetrahydropyrimidine nucleus. Reagents of this type are particularly simple to prepare and are very effective corrosion inhibitors. We have :found, however, that equally effective compounds result when the relatively high molecular weight hydrocarbon group occurs as a substituent of one of the nitrogen atoms, or of a.

relatively smallworganic radical attached to one 'cal having from 8-to 32 carbon atoms.

The preparation of"tetrahydropyrimidines sub- *stitutedin the,2-position by hydrocarbon radicals is well described-in the literature and is readily 'carriedout by reactionbetween a monocarboxylic acid :and a -diamine, or a *po'lyamine, containing at'leastpne primary amino group, and atlea'st onesecondary aminogroup, or another primary "amino group separated from the first primary amino group'by three carbonatoms. This reactionis generally carried out 'byheating the reactants toatemperature-of 230 C. orhigher, usually within-the range of 250 to 300 (3., at which tem- "peratures water is "evolved and ring closure is effected. For details of the preparation of'such reagents, see "German-Patent 700,371, datedDe- 'cember 1'8, i940; to EdmundWaldma-nn and August Chwala; GermanPatent'YOLSZZ, datedjJanuary 14, 1941toKar1'Miescher, Ernst Urech, and

KWilIiKIarar; and U. "SJ'Patent 2,194,419, dated March 319, 1940, ;to August Chwala.

When a-monocarboxylic acid containing 19 or more'carbonatoms isemployed in the above described synthesia'the resulting tetrahydropyrim hydrocarbon radical containing 8 ormore carbon atoms. LSuitable corrosion preventive reagents may, therefore'be made directly by reaction .of carboxylic acids such as oleic acid,,linoleic,acid,

linolenic acid; erucic acid, tall oil ffatty acid,

naphthenic acid, :nonoic acids, alpha-naphthylacetic "acid, *abi'etic acid, crude pine rosin acids,

-and-the*like with suitable *aminessuch as those enumerated below: I

" Examples =of amines'suitable for this synthesis "include lgS-propylenediamine, -dipropylene triamine, lg3-d-iaminobutane, 'zg i diaminopentane,

-ethyl-tri-methylenediamine, N- aminoethyl-tri- .-methylene =diamine, aminopropyl stearylamine,

tripropylenetetramine, tetrapropylenepentamine, high boiling polyamines prepared by the condensation of 1,3-propylene dichloride with ammonia, and similar diamines or polyamines in which there occurs at least one primary amino group separated from another primary or secondary amino group by three carbon atoms.

The preparatin of tetrahydropyrimidines substituted in the 2-position by a relatively high molecular weight hydrocarbon radical is exemplified by the reaction between oleic acid and 1,3-diaminobutane. If one molecular equivalent of oleic acid is reacted with one mole of 1,3-diaminobutane at a temperature of about 250 C. to 300 0., two moles of water are evolved, the re- "action proceeding as shown in the equations below to form a mixture of 2-heptadeceny1, 4- methyl tetrahydropyrimidine and Z-heptadecenyl, G-methyl tetrahydropyrimidine.

CHEM-000E NH2.CH2.0H2.CH.CH3

We have discovered that equally suitable corrosion preventive reagents may be obtained by introducing into the tetrahydropyrimidine molecule a hydrocarbon group of proper size as a portion of the substituent attached to the l-nitrogen atom of the ring or as the substituent of the 1- nitrogen atom of the ring. Where the aliphatic hydrocarbon group occurs in this position it is unnecessary that the 2-carbon atom substituent contain 8 or more carbon atoms. It may be, in fact, only a hydrogen atom or a methyl group, ethyl group, phenyl group, or other relatively sma11 hydrocarbon groups, although it is not restricted to such small groups. The preparation of the tetrahydropyrimidine compounds in which the higher molecular weight hydrocarbon radical occurs as a portion of the nitrogen atom substituent is also readily carried out by methods analogous to those already described. In this case, however, a number of alternative procedures are possible. For example, one may prepare Z-methyl, 1-octadecy1 tetrahydropyrimidine by reaction of octadecyl aminopropylamine with acetic acid at a temperature of about 250 C. to 300 C. until two moles of water are evolved for every mole of acetic acid employed. The same reagent may be prepared by the reaction of 2-methyl, tetrahydropyrimidine with octadecyl bromide followed by separation of the resulting alkylation products to isolate the desired compound.

Particularly suitable for the synthesis of tetrahydropyrimidines having a high molecular weight hydrocarbon group attached to the l-nitrogen of the ring or present as a portion of the l-nitrogen substituent, are the high molecular weight N-substituted propylenediamines and dipropylenetriamines. Some of the former are commercially available products, exemplefied by N-aminopropyl stearylamine, which may be readily prepared by condensation of acrylonitrile,

with a high molecular weight amine, such as stearylamine, followed by hydrogenation and separation of the diamine. Analogous diamines derived from cetylamine, crude tall oil amine, abietylamine, oleylamine, dodecylamine, and similar are suitable for synthesis of the present corrosion inhibitors.

As stated above, our invention contemplates, in its broadest aspects, the use of tetrahydropyrimidines of the formula type where the symbols have their previously described meaning. In these reagents, generally at least three occurrences of B will be hydrogen atoms. In the more common reagents D will be a relatively small divalent organic radical composed of elements from the group consisting of C, N, O, and H, and may be a hydrocarbon group, an alkyleneamido group, an alkyleneamino group, a substituted acetyl group, and the like, such as are illustrated in the following examples where n is the numeral 1 to 6, or where -CnH2nas a whole represents a divalent hydrocarbon radical containing from 1 to 6 carbon atoms and which may be aliphatic, cycloaliphatic, aromatic, or mixed in character, and where R, as before, is hydrogen or a hydrocarbon radical.

We have found that particularly effective corrosion preventive reagents result when the tetrahydropyrimidine compound contains basic nitrogen groups in addition to those nitrogen atoms inherent to the tetrahydropyrimidine ring. In general, compounds of this type are those in which the basic nitrogen group is contained in the radical D in the above formula. Examples of the radical D, where it contains basic nitrogen groups, are as follows:

mam-029 fiwwhim fihe hyrlmearbongmup enntshining fmm a-mem, 4emethyltetrhhydmpyrimidine 20 a rt-$01 013:

Examples .df suitable corrosion ,preventives GET-CL NC o nHHO-iC- CMHu :hsteroyloxye'thyl, ephenyltetwhydropyrtmidine marempress,idf arm-rosinrrpreventives useful in' the upraetlce @df ithe "-present mverition whih "contain 6 music mitragen groups memes iibhuse :m *the inlueflre 'fdllowing: 410. N-Dflu lxlipmpyleuediammm Zwyc'lupentylpmpyltetramydropyrimidime A1fih0llgh-We.haVB.Sh0WI1- ab0Vfi the compcsition .of .a number ..of effective inhibitors wnmn :are tetmhydropyrimidmes containing at least one hydrocarhonradicalhaving lfr0m 8 to B'Qeaihon atoms, :we should like 300 :pointwut .that, ageneral the most refiectiverreagents, andrthosechaving the most desirable xsolubility .chara.cteristics rare .thnse :in which the hydrocarbon group econtams from 10 to 20 carbon atoms. QEXamDIBSDfiSIIGH ,preferred 5 groups are deey1,-b1eyl, abietyl, :stearyl, and -.the like.

' The corrosion preventive products of themesent invention, sinc they cantaima :tetrahydropyrimidine ringrmayyin general, be .alkylaized to form either .-a .l-ralkylesubstituted tetrahydmpyrimidine, or.a.qua.temary.ammonium salt, where the alkyl group is attached .to -eithe1uonboth ;the 1 and 3 ni-trngen atoms. Eur example, vusing eetyl bromide :as .a typical alkylating agent, the

gInstead of the cetyl bromide, used in the examples above, one may use other alkylating agents such as methyl bromide, benzyl chloride, ethyl sulfate, dichloroethyl ether, chloroparaffin, etc., to obtain equally suitable derivatives of tetrahydropyrimidines which may be employed in the present process.

Although we have described the corrosion inhibitors of our process as tetrahydropyrimidines, we may, in many instances, employ these compounds in the form of their salts, either with organic or inorganic acids. Being relatively strong bases, the tetrahydropyrimidines readily formsuch'salts', and where the reagent contains basic groups in addition to the tetrahydropyrimidine ring nitrogen atoms, they may form dior polysalts. Examples of acids which may be used to form such salts are hydrochloric acid, sulfuric acid, acetic acid, glycolic acid, oxalic acid, maleic acid, oleic acid, abietic acid, phosphoric acid, petroleum sulphonic acid, naphthenic acid, rosin,

'phenylacetic acid, benzoic acid and the like.

'Salts of the tetrahydropyrimidines, such as those above described, appear to be equally as effective as the free bases. Probably, in the dilute solutions in whichthey are employed as corrosion inhibitors, the salts hydrolyze or otherwise decompose to some extent and reach an equilibrium with the acids and other constituents of the corrosion medium.

While we have described our corrosion inhibitors as tetrahydropyrimidines and have illustrated themabove as single ring compounds, it

should be pointed out that in some instances reagent compounds containing two or more heterocyclic rings, such as two tetrahydropyrimidine rings may be employed. For example, if one reacts one mole of tripropylenetetramine with a mole of stearic acid to form a substituted hepta- 'decyltetrahydropyrimidine, and then reacts this further withanother mole of a carboxylic acid at a suitable high temperature, a ditetrahydropyrimidine is obtained.

'lripropylenetriamine N- C H2 Cl7H35-COOH+CHLO0OH --v C17H35.C CH2 Stearlc acid Acetic acid NC H2 N-C H2 CH 0 Hi N-CHz Such ditetrahydropyrimidine are intended to be included when reference is made to substituted tetrahydropyrimidines herein or in the claims.

Many obvious simple derivatives of the herein described corrosion inhibitors may be prepared which are also effective. For example, we have defined the group R in the structural formulae above as being a member of the class consisting of hydrogen, and hydrocarbon groups. Actually,

the use of'halogenated hydrocarbon groups appears to yield equally effective reagents, and chlorohydrocarbon groups, particularly, are readily introduced during synthesis. Since the chlorine atomsin these groups are relatively nonreactive and yield products with solubilities similar to the hydrocarbon derivative, they do not differ greatly in behavior from the corresponding hydrocarbon derivative.

The method of carrying out our process is relatively simple in principle. The corrosion preventive reagent is dissolved in the liquid corrosive medium in small amounts and is thus kept in contact with the metal surface to be protected. Alternatively, the corrosion inhibitor may be applied first to the metal surface, either as is, or as a solution in some carrier liquid or paste. Continuous application, as in the corrosive solution, is the preferred method, however.

The present process finds particular utility in the protection of metal equipment of oil and gas wells, especially those containing or producing an acidic constituent such as HzS, CO2, organic acids and the like. For the protection of such wells,

.' the reagent, either undiluted or dissolved in .a

suitable solvent, is fed down the annulus of the well between the casing and producing tubing where it becomes commingled with the fluid in the well and is pumped or flowed from the well with these fluids, thus contacting the inner Wall of the casing, the outer and inner wall of tubing, and the inner surface of all well-head fittings, connections and flow lines handling the corrosive fluid.

Where the inhibitor composition is a liquid, it is conventionally fed into the well annulus by means of a motor driven chemical injector pump, or it may be dumped periodically (e. g., once every day Or two) into the annulus by means of a so-called boll weevil device or similar arrangement. Where the inhibitor is a solid, it may be dropped into the well as a solid lump or stick, it may be blown in as a powder with gas, or it may be washed in with a small stream of the Well fluids or other liquid. Where there is gas pressure on the casing, it is necessary, of course, to employ any of these treating methods through a pressure equalizing chamber equipped to allow introduction of reagent into the chamber, equalization of pressure between chamber and casing, and travel of reagent from chamber to well casing.

Occasionally, oil and gas wells are completed in such a manner that there is no opening between the annulus and the bottom of the tubing or pump. This results, for example, when the tubing is surrounded at some point by a packing held by the casing or earth formation below the casing. In such wells the reagent may be introduced into the tubing through a pressure equalizing vessel, after stopping the flow of fluids. After being so treated, the well should be left closed in for a period of time sufficient to permit the reagent to drop to the bottom of the well.

For injection into the well annulus, the corrosion inhibitor is usually employed as a solution in a suitable solvent, such as mineral oil, methylethyl ketone, xylene, kerosine, or even water. The selection of solvent will depend much upon the exact reagent being used and its solubility characteristics. It is also generally desirable to employ a solvent which will yield a solution of low freezing point, so as to obviate the necessity of heating the solution and injection equipment during winter use.

For treating wells with packed-oil tubing, the use of solid sticks "or plugs of inhibitor is especially convenient". These may be prepared by blending the inhibitor with a mineral wax, asphalt or resin in a proportion sufficient to give a moderately hard and high-melting solid which can be handled and fed into the well conveniently.

The amount of corrosion preventive agent required in our process varies with the corrosiveness of the system, but where a continuous or semicontinuous treating procedure is carriedout as 9;.- deserihed above... the: addition 013:; reagent.- in the proportion of from one partner: 14,001) to: one; M12 per 20.0110 or more; parts of oormsivenuid. will generally'provjde; protection.

liner. effectiveness of: the; herein. described no agents for the prevention-of corrosion; is illustrated by the data of. the following table. These data show the reduction in attack of mild steel by 1% hydrochloric acid by various tetrahydropyrimi-dines over a rangeiofconcentrations. Duplicate weighed mild steel plates were immersed in 1% hydrochloric acid. solution of the reagent shown for a period of 24 hours" at a temperature off'28 (2., after which theywere removed; washed again weighed. The loss in weight is expressed as the percentage ofthe loss in, weight of" the plates, in 1% hydrochloric acid containing no inhibitor:

The protective action of the herein described reagents appears to bepmaintained for an appreciable time after treatment ceases, but eventually is lost unless another application is made.

For theproteetibn ofgas wells andgas-cond'ensatewells; the amount of corrosion inhihitor-re-- quired will usually be within the range of one half to3 lbs. per million cubic feet of gas pro-- duced, depending'upon the amounts and composition of corrosive agents in the gasand the amount of liquid hydrocarbon and water pro d-ucedi However; in no case does the amount of inhibitor required appearto he stoichiometrically related to the an'lountof acids produced by: a well since protection is: obtained with much less. tetrahydropyrimidine than usually would be requiredforneutralization of the acids produced;

Recapitulating, we have found that the corrosion of metals, and particularly ferrous metals, may be inhibited by the application thereto of a substituted tetrahydropyrimidine in which a substituent at either or both the 1- or 2-position oi the ring contains a hydrocarbon group havingfrom S te 32 carbon atoms. Of thisbroad genus: of corrosion inhibitors; there are several suit-- classes which may be employed effiectivelyour process. Such sub-classes are; (-1) those: in. which the 1-position substituent contains. amino group, (2) those in which the I-position substituent is free of amino groups, (3) those in which the 4: and/or and/or d-position ring carbons are substituted; etc.

Having: thus described our invention, what we claim as new and desire to secure by Letters Patent, is-

1. A process for'preventingcorrosion of metals including the step of applying to such metals a substituted" tetrahydropyriinidine of the formula type:

N--OB2 CB3- NYC21 t where I) is a member of the classconsisting D"-R and R; D represents a divalent organic Ht radical; containingless than: 25.1 carbon: atoms. composed of elements. from; the; gro p nsisting; of; G, H, O and N; R is; a. member. of: the. class. consisting of hydrogen. and. hydrocarbon radi- BE isa member. ot the. clacscens and hydrocanbonl radicals. cont 7 carbon atoms, with the proviso that, at least: three occurrences of B be hydrogen.

2. A process for preventing corrosion of ferrous metals including the step of applying to such metals a substituted tetrahydropyrimidine of the formula type:

wherez'D. is. a. member the class consisting of D' -R. and R; D. represents a divalent organic: radical; containing less than 25 carbon atoms composed of elements from the group consisting; ofi C, .H, O; and N; R is. a member of the class consisting of: hydrogen and hydrocarbon. radicals with the proviso; that; at: least one occurrence.- of R contains from 3 to 32 carbon atoms; 33. is, a member of the; class consisting of hydrogen and hydrocarbonradicals containing less'than 7' carebon a'tcmris with; the. proyiso that. at least three occurrences of B be hydrogen.

3. A process for preventing corrosion of ferrous metals including the. step of applying to such metals a substituted tetrahydropyrimidine of the formula type NG B 2 R; of 0 B17 lTT-Q B2 D Where D is a member of the class. consisting of- D.'-R. and, R; D. represents. a divalent. organic radical containing less than 25. carbon atoms. composed of, elements from the group. consisting of C, H,. Qand. N; Ris a member of theclass.

consisting of hydrogen and hydrocarbon radicals. with-the, proviso that at least one occurrence, of R, contains from 10 tom. carbon atoms; B. is a, member of. the class, consisting of hydrogen and hydrocarbon radicalscontaining. less than 7 car.- honJ atoms, with, the. proviso that at least. three occurrences of B, be hydrogen.

4. A process for preventing corrosion of ferrous metals including the, step of aplyh'ig to such metals 2-heptadecyl, 6-methyltetrahydropyrimidine.

5. A process for preventing corrosion of ferrous metals. including the step of applying to such metals l-01eylamidoethyltetrahydropyrimidine.

6. A process for, preventing corrosion of ferrous metals in l ding the t p oi pply to such metals av substituted tetrahydropyrimidine of the. formula typ where D is a member of; the class consisting of D.-R and R; D represents a divalent organic radical containing less than 25 carbon atoms.

composedof elements from the group consisting of" C, H; O and N and containing at least one. amino group; R is a member of the class consisting of hydrogen and hydrocarbon radicals, with the proviso that at least one occurrence of R contains from to carbon atoms; B is a member of the class consisting of hydrogen and hydrocarbon radicals containing less than '7 carbon atoms, with the proviso that at least three occurrences of B be hydrogen.

'7. A process for preventing corrosion of ferrous metals including the step of applying to such metals a substituted tetrahydropyrimidine of the formula type:

N-CH:

where D is a member of the class consisting of D R and R; D represents a divalent organic radical containing less than carbon atoms, composed of elements from the group consisting of C, H, O and N and containing at least one amino group; R is a member of the class consisting of hydrogen and hydrocarbon radicals, with the proviso that at least one occurrence of R contains from 10 to 20 carbon atoms.

8. A process for preventing corrosion of ferrous metals including the step of applying to such metals Z-heptadecenyl, 1-aminopropyltetrahydropyrimidine.

9. A process for preventing corrosion of oil and gas well equipment, including the step of injecting into the well a substituted tetrahy-dropyrimidine of the formula type:

where D is a member of the class consisting of DR and R; D represents a divalent organic radical containing less than 25 carbon atoms, composed of elements from the group consisting of C, H, O and N; R is a member of the class consisting of hydrogen and hydrocarbon radicals, with the proviso that at least one occurrence of R contains from 8 to 32 carbon atoms; B. is a member of the class consisting of hydrogen and hydrocarbon radicals containing less than 7 carbon atoms, with the proviso that at least three occurrences of B be hydrogen.

10. A process for preventing corrosion of oil and gas well equipment, including the step of injecting into the well a substituted tetrahydropyrimidine of the formula type:

where D is a member of the class consisting of D'--R and R; D represents a divalent organic radical containing less than 25 carbon atoms, composed of elements from the group consisting of C, H, O and N; R is a member of the class consisting of hydrogen and hydrocarbon radicals, with the proviso that at least one occurrence of R contains from 10 to 20 carbon atoms; B is a member of the class consisting of hydrogen and hydrocarbon radicals containing less than 7 carbon atoms, with the proviso that at least three occurrences of B be hydrogen.

11. A process for preventing corrosion of oil and gas well equipment, including the step of injecting into the well 2-abietyltetrahydropyrimidine.

12. A process for preventing corrosion of oil and gas well equipment, including the step of where D is a member of the class consisting of DR and R; D represents a divalent organic radical containing less than 25 carbon atoms, composed of elements from the group consisting of C, H, O and N and containing at least one amino group; R is a member of the class consisting of hydrogen and hydrocarbon radicals,

. with the proviso that at least one occurrence of R contains from 10 to 20 carbon atoms; B is a member of the class consisting of hydrogen and hydrocarbon radicals containing less than 7 carbon atoms, with the proviso that at least three occurrences of B be hydrogen.

14. A process for preventing corrosion of oil and gas well equipment including the step of injecting into the well a substituted tetrahydropyrimidine of the formula type:

N-CH2 r -on,

where D is a member of the class consisting of DR and R; D represents a divalent organic radical containing less than 25 carbon atoms, composed of elements from the group consisting of C, H, O and N and containing at least one amino group; R is a member of the class consisting of hydrogen and hydrocarbon radicals, with the proviso that at least one occurrence of R contains from 10 to 20 carbon atoms.

15. A process for preventing corrosion of metals including the step of applying to such metals a carboxylic acid salt of a substituted tetrahydropyrimidine of the formula type:

N-GB, CB2 \NC2 1') where D is a member of the class consisting of D--R and R; D represents a divalent organic radical containing less than 25 car-bon atoms,

composed of elements from the group consisting of C, H, O and N; R is a member of the class consisting of hydrogen and hydrocarbon radicals, with proviso that at least one occurrence of R contains from 8 to 32 carbon atoms; 13 is a member of the class consisting of hydrogen and hydrocarbon radicals containing less than 7 carbon atoms, with the proviso that at least three occurrences of B be hydrogen.

CHARLES M. BLAIR, JR. WILLIAM F. GROSS.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A PROCESS FOR PREVENTING CORROSION OF METALS INCLUDING THE STEP OF APPLYING TO SUCH METALS A SUBSTITUTED TETRAHYDROPYRIMIDINE OF THE FORMULA TYPE. 